DESCRIPTION (Taken from application) The goal of the proposed research is to develop a mechanistic understanding of the processes contributing to phytoremediation of soils contaminated with complex mixtures of polycyclic aromatic hydrocarbons (PAHs) and metals. Specific focus will be on pyrene and benzo[a]pyrene co-occurring with chromium, arsenic, nickel, cadmium, and lead. The approach takes into consideration both the ability of the plant to remove contaminants from the soil, as well as the ability of the plant to change degradative soil biofilms through the release of root exudates. The effect of metal and PAH availability in the soil will be monitored by soil extraction and bioindicators, throughout these investigations. The specific aims are: (1) to investigate potential mechanisms controlling phytoremediation, including uptake, rhizosphere degradation, and bioavailability, (2) to characterize root exudates and identify the specific components that enhance PAH degradation, and (3) to examine variation in root exudate production across plant species and under differing environmental conditions. The results of the experiments conducted under the above specific aims will allow the discernment of the extent to which either uptake or input (to the rhizosphere) is responsible for soil remediation in the presence of plants. It will also be possible to determine if concurrent phytoremedial processes operate in an additive, synergistic or antagonistic manner in soils contaminated with metals, PAHs, or mixtures of these. By identifying the specific exudate components that enhance PAH degradation, we will have a basis for screening plants for use in phytoremediation . This information will be directly applicable to the management of actual Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) (Superfund) sites and will further the development of phytoremediation as an in situ technology. In addition, the role of bioavailability will be examined here after we validate that our methods are providing an accurate estimate. Validated soil extraction methods for determination of bioavailable soil metals and PAHs will be a significant contribution to the tools needed for effective soil remediation and site assessment.